Underwater transducer



March W, 1970 D. J. BOZICH 5 3 UNDERWATER TRANSDUCER Filed Oct. 15, 1968 .4 Sheets-Sheet 1 /NVN7'O/? DANIEL J. BOZ/CH mwuj 4 W March W, 3W0 D. J. BOZICH UNDERWATER TRANSDUCER .4 Sheets-Sheet 2 Filed Oct. 15, 1968 A FOR/V5 v5 March 19, 1970 D. .1. BOZIQH 3,500,304

UNDERWATER TRANSDUCER Filed Oct. 15, 1968 .4 Sheets-Sheet 3 lA/l/EA/TOA 0AML z 502/01 MLL W A FOR/V15 Y5 arch 10, 1970 D. J. BOZICH 3,500,304

UNDERWATER TRANSDUCER Filed Oct. 15, 1968 .4 Sheets-Sheet 4 f5. -LN 4 41m A 77'OR/VE Y5 3,500,304 UNDERWATER TRANSDUCER Daniel .I. Bozich, Huntsville, Aia., assignor to Wyle Laboratories, El Segundo, Calif, a corporation of California Filed Oct. 15, 1968, Ser. No. 767,637 Int. Cl. H041 17/00 US. Cl. 340-9 6 Claims ABSTRACT OF THE DISCLOSURE The radiating surface of an underwater transducer is provided by the edges of a plurality of elongated structural members which are placed adjacent to one another. Each structural member has a plurality of electrostrictive elements placed on both sides of the web portion thereof and which are spaced therealong. A conductive sheet serving as a first electrode is placed between each two adjacent structural members so that it is contacted by electrostrictive elements on adjacent structural members. The structural members are conductive and serve as the second electrode.

BACKGROUND OF THE INVENTION The invention described herein relates generally to the generation and/ or reception of wide-band acoustic pressures within liquid media or, more particularly, to a specific means for the design, construction and operation of underwater wide-band acoustic transducers.

The frequency response spectra of the pulsating underwater acoustic transducers described herein are dependent upon the overall dimensions of the radiating surfaces and the mechanical properties of the dynamic transducer structures which determine the radiation impedance characteristics of the coupling between the surfaces and the acoustic medium, and the mechanical impedance properties of the structures driving the transducer surfaces, respectively. The response bandwidth of each specific transducer design is sensitive to the proper matching of the radiation impedance of the pulsating transducer surface and the overall mechanical impedance of the driven transducer structure. The overall size of the radiating surface area determines the operating frequency regime of each specific transducer.

The radiation reactance mass adds positively to the structural mass of the pulsating surface thus significantly lowering the resonant frequency of a properly designed transducer and has a characteristic rapid decrease in mass load with increasing frequency over a fairly broad frequency band. The radiation resistance on the other band is increasing with increasing frequency over the same broad frequency band as for the reactance mass load. The net result is a fairly fiat efficient high-power broadband response spectrum from a lightweight underwater sound source and, reciprocally, a broad-band hydrophone.

OBJECTS AND SUMMARY OF THE INVENTION An object of this invention is the provision of an underwater transducer which can operate over a wide frequency band.

Another object of the present invention is the provision of an underwater transducer which operates efficiently.

Yet another object of the present invention is the provision of an underwater transducer which can provide a high power output.

Still another object of the present invention is the provision of a novel construction for an underwater transducer utilizing principles whereby different shapes may be obtained for said underwater transducer.

These and other objects of the present invention are 3,500,304 Patented Mar. 10, 1970 achieved in the modular construction of a cylindrically shaped transducer, which is shown and described by way of example. The cylinder wall is made to pulsate radially. This is achieved by constructing the cylinder wall out of a plurality of elongated members which are called beams. These are fitted together to form the cylinder. The beam walls have piezoelectric ceramic elements attached thereto, so that they are interspersed between adjacent beams and provide the radial driving forces to the beams. The ends of the cylinder are capped by rigid end plates and the cylinder wall is surrounded by a rubber skin which also acts as a seal to enable underwater operation.

The novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The invention itself both as to its organization and method of operation, as well as additional objects and advantages thereof, will best be understood from the following description when read in connection with the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a view of an embodiment of the invention with the side wall partially removed in order to show the internal construction thereof;

FIGURE 2 is a view in section of the invention along the lines 22 of FIGURE 1;

FIGURE 3 is a view of the top plate of the underwater transducer in accordance with this invention;

FIGURE 4 is a view of the bottom plate of the underwater transducer in accordance with this invention;

FIGURE 5 is an enlarged cross-sectional view of a beam element employed in the Wall of the transducer;

FIGURE 6 is a plan view of a typical spherical triangle transducer which illustrates another arrangement made possible by using the principals of this invention;

FIGURE 7 is a view in section along the lines 7-7 of FIGURE 6;

FIGURE 8 is a view of a typical structural element and electrostrictive element assembly;

FIGURE 9 is a side view of FIGURE 8; and

FIGURE 10 illustrates a bus bar used in the invention embodiment shown in FIGURE 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS By way of example of the embodiment of the invention, and not to be construed as a limitation upon the invention, there 'will be first presented herein a description of the construction details of a cylindrical transducer, which will assist in an understanding of the invention. Thus, FIGURE 1 is a detailed drawing of the transducer assembly in accordance with this invention, and FIGURES 2 through 5 show constructional details thereof. An embodiment of this invention which was built had an active surface dimension envelope of 30 outside diameter, by 30" length. The active surface of this assembly consisted of 60 vertical contoured beams 10 forming an open cylinder to the side walls of which approximately 1800 1" x 1" x /2 lead zirconate ceramic blocks 12 are bonded. The bonding is with a hard conducting cement and occurs at a mean radius from the center of the cylinder of substantially 13.4". In FIGURE 2, which is a cross-sectional view along the line 22 of FIGURE 1, there may be seen a cross-section of the beams and the manner in which the ceramic blocks 12 are attached thereto. FIG- URE 5 is an enlarged view of the cross-section of a beam with ceramic blocks attached on either side of the center portion of the beam.

As may be seen in FIGURES 2 and 5, the beam has a somewhat I shape with the base of the I which forms the outer wall of the cylinder having offset extending portions, respectively 14, 16, for locking with the mating 3 portions of adjacent beams. Also, the center portion or web 18 of the I has notches to which the ceramic blocks can fit. The beam may be formed of extruded aluminum.

In the embodiment of the invention which was built, the beams were assembled to form a cylinder 30" outer diameter by 23 inner diameter by 30 long. Adjacent beams are separated by copper bus bars 20 which are almost co-extensive with the beams. The bus bars extend between the ceramic blocks, thus providing a rugged unitized construction. Each bus bar contacts the ceramic blocks mounted on the beams on either side of the bus bar. There are about three square inches of surface area per square inch ceramic cross-sectional area. The ceramic blocks are silvered on their two opposite I" by 1 faces and are polarized to permit a maximum applied voltage of 30,000 volts peak-to-peak for linear response. The bus bars are interconnected at each end by fiexible copper straps (not shown), which inturn are connected to the strap 22 and serve as one potential applying electrode to the ceramic blocks. Each end of each beam is connected by a compliant stainless steel strap 24 to the cover plate 26. The cover plate is also connected to a strap 28. The straps 22, 28 are respectively connected to feed through terminals 23, 29.

The compliant stainless steel straps 24 which connect the beams to the cover plate permit radial motion of the beam cylinder assembly without being constrained relative to the transducer supporting structure. This also allows all of the beams to acquire the same ground potential.

All metal surfaces which may be in contact with water are made of corrosion resistant stainless steel. The cover plate 26 has an opening therethrough which is covered by a small cover plate 30. The small cover plate 30 is bolted onto the cover plate 26. The small cover plate 30 has an opening therethrough which supports a plug 31 through which the feed-through terminals pass. An opposite plug 32 fits into a cable entry hatch formed by a metal tube 35 welded to the top of the small cover plate. The power cable 36 connects to this plug 32. The plug 32 is held in place by a sealing plug 37 which is thread ably fitted onto the metal tube 35. The cover plates 26 and 30 are machined from 1 inch stainless steel.

As shown in FIGURE 1, a stainless steel tube 40 which has a 12" internal diameter by 1" wall thickness serves as a center support. It is welded to the bottom plate 42 and a flange 44 is welded to the top of the tube 40. The top cover plate 26 is sealed with an O ring 48 when it is bolted to the flange 44 by bolts 50. The center of the tube 40 is left open to the water to reduce the buoyancy of the transducer.

A swivel bolt assembly 52 is centered and Welded to the top cover plate for lifting and lowering the transducer and also for lifting the top cover plate for assembly or disassembly of the transducer. The swivel prevents twisting of the power cable by allowing support cables to untwist. The complete assembly may be flushed with nitrogen gas through a gas inlet and exhaust valve 44. This assures completely dry operating conditions and precludes sparking due to moisture.

The outer cylindrical surface of the beams is covered with a cylindrical impedance compatible rubber diaphragm which is fastened to the top and bottom cover plate by means of compression bands 62, 64- respectively. A stainless steel grid 66 is provided around the outer surface to prevent damage to the rubber. Mounting lugs 68 are bolted in spaced locations around the top and bottom cover plates, and serve to hold the stainless steel grid in place. Legs 70 are welded to the bottom cover plate and serve to prevent damage to the screen and to the rubber during the course of transit of the transducer.

The transducer is horizontally omnidirectional below about 2000 cycles per second. It operates efiiciently over a frequency range of at least two octaves, covering a frequency range from 100 cycles per second to over 10,000 cycles per second. Its use of the reactance mass load to obtain low frequency operation instead of actual structural dynamic mass affords a lighter, cheaper and more efiicient transducer.

From the modular construction of the transducer, it should be appreciated that other transducer shapes may be made, which have not been heretofore obtainable. This can be done by forming the beams into suitably shaped arcs and shortening their lengths if required to preserve their response and enable them to comform to a desired peripheral shape. For example, as shown in FIGURES 6 through 10, an equilateral spherical triangle transducer may be made. A spherical triangle is a radial projection of an equilateral triangle on a circumscribing sphere. This can be used to form the sides of a regular polyhedron such as a tetrahedron, octahedron, or an icosahedron.

FIGURE 6 is a plan view of the equilateral spherical triangle,

FIGURE 7 is a view in section along the lines 7-7,

FIGURE 8 illustrates the structure of an element on both sides of which ceramic wafers are attached,

FIGURE 9 is an end view of this element, and

FIGURE 10 represents a copper bus bar used with the element shown in FIGURE 8.

The spherical triangle 72, shown in FIGURE 6 is built up of arcuate beams '74 which have ceramic wafers 76, cemented on opposite sides of the element 74, at spaced locations therealong. Each of the elements ends in a terminal portion 75, which has a hole therethrough so that it can be connected to an adjacent element if required.

The ceramic wafers are conductively attached to the element 74. As may be seen in FIGURE 7, to insure hat there is no difference in potential between adjacent elements, straps 78 are connected between adjacent elements. As may be seen in FIGURE 10, an arcuate copper sheet 80 is used as the opposite electrode for applying potential to the ceramic wafers which are attached to an arcuate beam member. These copper sheets are also glued conductively to the outside sides of these ceramic wafers and are connected together by straps. The top ends of the beams and the copper electrodes are connected by leads respectively 82, 84 to a pressure proof stufiing box cable disconnect plug assembly 36. If desired, a lifting bolt assembly 88 is provided.

It should be appreciated, that the beam members carrying ceramic wafers are placed so that the ceramic wafers on adjacent beams are spaced by a common copper electrode which is conductively connected to adjacent ceramic wafers. Of courre, the outer surface of these beam members is covered with a compatible impedance rubber diaphragm in the manner shown for the cylindrical form of the transducer, which may be in turn protected by a wire cage if needed.

Upon the application of electrical excitation to the transducer, the ceramic wafers will change dimensions in well known manner to compress the beam member causing it to change dimensions radially whereby the surface of the transducer expands or moves outwardly. The surface is restored to its original shape upon the removal of the excitation.

Transducer surface shapes other than triangular may be fabricated using the techniques set forth by this invention. For example, one can make spherical squares, which are the projections of the sides of a cube on the surface of a circumscribing sphere, or regular spherical pentagons, which are the projections of the sides of the dodecahedron on the surface of a circumscribing sphere. The manner in which these may be fabricated is similar to the manner in which the triangular elements shown in FIGURES 6 through 10 were fabricated, except for the replacement of the spherical triangles by either a spherical square or a spherical pentagon.

Other geometrical shapes may be fabricated if desired using the concept of attaching a large number of electrostrictive elements to active vibratory structural members which are then built up to produce the transducer shape. The transducer thus constructed provides a broad operational bandwidth whereby it may be used not only for the normally understood uses of transducers in connection with sonar, but also can be used for communication using voice frequency transmission and in the reception of acoustic signals as a hydrophone. Because of the increased power output obtainable using the basic construe tion in accordance with this invention, the range of underwater communication may be considerably increased.

There has accordingly been described and shown herein a novel, useful and unique structure for an underwater transducer.

What is claimed is:

1. An underwater transducer comprising a plurality of structural elements positioned adjacent one another to form a radiating surface for said transducer, each said structural element having a top and bottom edge separated by a center web portion, said center web portion being elongated and having notches on opposite sides thereof and spaced therealong, the radiating surface of said transducer being formed by abutting top edges of said elements, a plurality of electrostrictive elements and means attaching a different one of said plurality of electrostrictive elements to said structural elements at a different one of said notches therein, bus bar means positioned between and in contact with the electrostrictive elements on adjacent structural elements, and means to apply a signal at a predetermined frequency to said bus bar means and to said structural elements to thereby cause vibration of said structural elements at said predetermined frequency.

2. Apparatus as recited in claim 1 wherein each of said structural elements is made of aluminum, and each of said electrostrictive crystals is made of polarized ceramic material.

3. Apparatus as recited in claim 1 wherein said radiating surface is covered by an impedance matching rubber membrane.

4. An underwater transducer having a curved radiating surface comprising a plurality of adjacent vibratory elements each of which comprises an elongated structural member having a top and bottom edge separated by a web, a plurality of notches on both sides of said web which are spaced from one another along said web, the top edge of each said structural member abutting the top edge of the adjacent structural member for forming a radiating surface for said transducer, an electrostrictive element attached to the notched portion of each member, bus bar means extending between and contacting the electrostrictive elements attached to adjacent vibratory elements, means applying electrical oscillations at a predetermined frequency to said bus bar means and to said plurality of vibratory elements to effectuate vibration thereof at said predetermined frequency.

5. An underwater transducer as recited in claim 4 wherein said plurality of radiating elements are arranged in a circle to provide a cylindrical radiating surface,

a supporting cylindrical member positioned centrally within the circle formed by said plurality of vibratory elements, means for attaching the bottom edges of said vibratory elements to said cylindrical member for being supported thereby,

cover plate means attached to said central supporting cylindrical member and enclosing the region between said central supporting member and said cylinder formed by said plurality of vibratory elements, and

an elastic membrane covering the surface provided by said plurality of vibratory elements.

6. An underwater transducer as recited in claim 4 wherein each said elongated structural member is curved along its elongation axis to provide a curved radiating surface for said plurality of adjacent vibratory elements which is at least a portion of a spherical surface.

References Cited UNITED STATES PATENTS 2,723,386 11/1955 Camp 34011 2,803,808 8/1957 Wallace 340-11 2,964,837 12/1960 Harris.

3,043,967 7/1962 Clearwaters.

RODNEY D. BENNETT, JR., Primary Examiner B. L. RIBANDO, Assistant Examiner U.S. Cl. X.R. 340-40 

